Vehicles, such as crawler tractors, are conventionally driven by a pair of drive units that respectively cooperate with the two tracks on opposite sides of the vehicle. For years, it has been customary to have two separate control levers respectively controlling the speed and direction of the two drive units on opposite sides of the vehicle.
More recently, various types of single handle control levers have been developed for simultaneously controlling the speed and direction of movement of the respective drive units by proper manipulation of the single handle control lever. Examples of such units are disclosed in Case, U.S. Pat. No. 3,431,993, and Gray, U.S. Pat. No. 3,792,744.
The above Gray patent discloses a single handle control system for a pair of hydraulically operated motors that drive two pairs of wheels respectively located on opposite sides of a vehicle. The single control lever is connected to control arms forming part of respective motors through rigid links so that movement of the control lever about one axis extending transversely of the vehicle will simultaneously move both control arms the same amount in the same direction while movement of the control lever about a second perpendicular axis entending longitudinally of the vehicle will move the respective control arms in opposite directions. Thus, the vehicle speed in the forward or reverse direction is controlled by moving the handle about the first pivot axis and the steering of the vehicle is controlled by moving the handle about the second pivot axis.
One of the problems encountered with a control unit of this type is that the operator must at all times maintain pressure on the control handle to keep the vehicle moving in a given direction at a given speed. This becomes extremely annoying, particularly when the vehicle is being transported between job sites.